Have you always wondered what that purple-flowering tree was, down the street? Or the one by the post office that turns bright yellow in fall?

Turn to a new book by Matt Ritter, a botany professor at Cal Poly San Luis Obispo, and you should have the answer in short order.

“A Californian’s Guide to the Trees Among Us” features 150 of the most common trees growing in urban and suburban areas across the state.

“Ninety-five percent of the trees are covered,” Ritter said, noting that these are trees that have been planted in neighborhoods, gardens, parks and along streets. There are a handful of California natives. But most of the trees living in what arborists call our “urban forest” are from Australia, East Asia and other temperate and subtropical regions of the world.

A Unique Approach

Valley oak (Quercus lobata)

Plenty of books have been written about trees. However, what makes Ritter’s distinct is the approach he offers to identify trees.

Readers can take two paths: flip through the pages until they find a photo that resembles what they’re trying to figure out. That’s generally an easy route, as each of the 150 trees gets a full page treatment, with more than 500 photos and illustrations of mature specimens and close-ups of leaves, bark, cones, flowers, seeds and other pertinent details.

Or the more scientifically inclined might follow Ritter’s keys.

Keys are well-known in botany. Books about native plants — the encyclopedic Jepson Manual in particular — go to great lengths to “key” individual species by posing a series of either/or questions that narrow the choices until an identification is made.

But according to Ritter, no book about commonly planted trees has ever done that.

“There are no keys for regular trees,” he said. “It’s difficult to do (create the keys) because you have to first of all know what you would see. .. It’s training as a botanist that got me the ability to do that.”

Female cone of a Cook pine (Araucaria columnaris).

Ritter’s keys include such deceptively simple either/or questions as “Are the leaves lighter green on the lower surfaces?” or “Are the leaves the same color on the upper and lower surfaces; fruit smooth?” Based on the answers, he identifies the species or refers the reader to increasingly specific keys, where the identification is ultimately made.

When you reach that moment for a particular eucalyptus, for example, he said, “Now all of a sudden, you know it’s a sugar gum, with smooth bark, orange blotches and a lighter color on the leaf. You can be confident you are looking at the same thing, because on page 57 you can see it.”

To make the process easier for novices, he suggests first keying a tree whose identity you already know. He even provides a ruler along the edge of the back cover to measure various attributes of mystery trees.

“I wanted the book to be readable and interesting for the beginner, people who are just starting to look at trees, all the way to a person who’s a curator of an herbarium who wants to know esoteric differences between acacias. I was trying to strike the balance,” Ritter said.

A Light-Hearted Touch

The many shades of sweetgum (Liquidambar styraciflua).

As a professor, Ritter knows his way around thick, technical botanic tomes. He’s also editor-in-chief of Madroño, an academic quarterly journal published by the California Botanical Society, a group comprised of university professors and researchers.

Yet he has taken a decidedly light — but sincere — tone with this book. Early on, Ritter writes, “This is a book about trees, made from the bodies of dead trees, and reading it is a poor substitute at best for experiencing these wonderful organisms directly and personally. Take it with you and walk out among the trees in your neighborhood.”

He tucks in tidbits about natural history, quotes and tongue-in-cheek lists.

For instance, “Magnolias are an ancient and primitive group of flowering plants that evolved at a time when Earth was covered primarily with ferns and conifers… These flowers evolved prior to butterflies and bees and were originally pollinated by beetles and other ancient insects.”

The many quotes include this one from humorist Jack Handy, “I think people tend to forget that trees are living creatures. They’re sort of like dogs. Huge, quiet, motionless dogs, with bark instead of fur.”

And this from French historian and educator Charles Rollin: “The highest and most lofty trees have the most reason to dread the thunder.”

Ritter has fun with his lists, too, such as “Hobo Trees: Common Trees along California’s Roadways and Railroad Tracks” and “The Ten Trees Most Likely to Trip You on the Sidewalk.”

Then there’s “California’s ‘Old-Timey’ Trees: Trees planted in California long ago and now regularly found near old home sites and missions.” The old-timers include such imposing giants as tree of heaven, bunya bunya tree, blue gum and Monterey cypress.

“Another whole goal is to look at things in a different way,” Ritter said. “That’s a plant palette that existed then that doesn’t exist anymore… Now, when you see an area on the side of a hill with an old blue gum and a Monterey pine, even though any evidence of a structure is long gone, you’ll know that an old house existed there because old timey trees are still there.”

What Else is Inside

Ginkgo or maidenhair tree (Ginkgo biloba)

Each plant entry starts with the tree’s botanic name and common name, along with its Latin translation, pronunciation, plant family, native location, leaf type, habit, shape, sex and height.

“The thing there on every page, the plant morphology, that came from a lot of observation,” Ritter said.

The descriptions benefit from his observations as well. For example, about the tulip tree, which grows more than 80 feet tall, he writes, “A long pole trimmer, brave climb, jet pack, or view from a three-story building may be necessary to observe these majestic blooms closely, but they are well worth the effort.”

What you won’t find, though, are planting instructions or pest and disease diagnoses. Ritter said he didn’t want to duplicate information readily available from other sources.

“As a botanist, the two questions are, ‘What is that thing in my yard?’ and ‘What’s wrong with it?’ Many other books address the second question. This book addresses that first question.”

He added, “My audience is people in urban and suburban environments in California who will pick up the book, flip through it, instantly recognize something around them… Then they’ll get sucked in. A lay person who has a burgeoning curiosity about trees. I want them to become more interested in trees, I want them to become defenders of trees, I want them to plant trees, I want them ultimately to be more interested in general about organisms and conservation and diversity.”

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About Matt Ritter

Author Matt Ritter ensnared in the massive, above-ground roots of the Moreton Bay fig tree that sits near the Santa Barbara Amtrak station.

Author of “A Californian’s Guide to the Trees Among Us,” Matt Ritter is a botany professor at Cal Poly San Luis Obispo. He is editor-in-chief of the California Botanic Society’s quarterly journal. He writes about lesser-known but worthy trees for Pacific Horticulture Magazine; has written natural history and field trip guides about San Luis Obispo, and numerous scientific papers; and contributed to botanical references, including the upcoming second edition of the “Jepson Manual: Higher Plants of California” and the “Flora of North America Project.”

He is also chair of the City of San Luis Obispo Tree Committee.

Ritter shot all of the photographs for this new book. He is particularly proud that while he featured many street trees, not a single automobile is pictured.

Ritter is a lively speaker. His next appearance on the Central Coast will be February 20 at the Morro Bay Museum of Natural History.

In addition to his work as a botanist, Ritter describes himself as “a woodworker, athlete, musician, gardener, and all-around likable guy.”

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Seeds of Wisdom

“A Californian’s Guide to the Trees Among Us”, by Matt Ritter, 2011, costs $18.95. It is available at most independent bookstores, including The Book Loft in Solvang, and online at www.heydaybooks.com.

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Copyright, Joan S. Bolton. All rights reserved. Reproduction of text or photos in any form is prohibited without written permission.